[www-scripts] Clang Attribute Doc Update: ERROR

[root via www-scripts]

UPDATING LLVM SOURCES
HEAD is now at 39fc4a0 [X86] Move ENCODEKEY128/256 handling from lowering to selection.
>From https://github.com/llvm/llvm-project
 * branch            master     -> FETCH_HEAD
   39fc4a0..a7e45ea  master     -> origin/master
First, rewinding head to replay your work on top of it...
Fast-forwarded master to a7e45ea30d4c9c3f66f44f0e69e31eac3a22db42.
CMake Error at CMakeLists.txt:3 (cmake_minimum_required):
  CMake 3.13.4 or higher is required.  You are running version 3.7.1


-- Configuring incomplete, errors occurred!